Discharge Capacity Of Electrode Research Articles

Electrochemical performances of AB 5-type hydrogen storage alloy modified with Co 3O 4

Anodic electrodes with the mixture of hydrogen storage alloys and different contents of Co 3O 4 (2%, 4%, 6% and 8%, mass fraction) powders were made. The effects of Co 3O 4 on the electrochemical performance of the alloy electrodes were studied. The constant charge-discharge tests show that the discharge capacity of alloy electrodes with Co 3O 4 significantly increases, and the maximum discharge capacities of electrodes with 2%, 4%, 6% and 8% Co 3O 4 are higher than the electrode with no Co 3O 4 by 0.83%, 4.86%, 7.18% and 9.21%, accordingly. Linear polarization (LP) and electrochemical impedance spectroscopy (EIS) tests suggest that charge-transfer resistance decreases by the addition of Co 3O 4. Cyclic voltammogram (CV), scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) tests indicate that Co 3O 4 can partly dissolve and experience a reversible oxidation-reduction process of Co to Co (OH) 2, leading to the improvement in the electrochemical performance of hydrogen storage alloy.

Synthesis and electrochemical performance of novel loose structured submicro/micro-sized NiSn x alloy composites for lithium batteries

An effective method of carbothermal reduction was employed to prepare spherical microcrystal NiSn x alloy powders from oxides of Sn and Ni used as anode materials for Li-ion battery. According to XRD, SEM and TEM analysis, the synthesized spherical NiSn x powders show a loose submicro/micro-sized structure and a multi-phase composition. The prepared NiSn x alloy composite electrode exhibits a stable discharge capacity of electrode is ca. 380 mAh g −1 at constant current density of 50 mA g −1, and can be retained at 350 mAh g −1 after 25 cycles. Moreover, NiSn x alloys exhibit excellent high rate performance, i.e. stable discharge capacities of 300–310 mAh g −1 and the coulombic efficiencies of 97.5–99.5% have been obtained at the current density of 500 mA g −1. The loose submicro-sized particle structural characteristic and the Ni addition in Sn matrix should be responsible for the improvement of cycling stability of NiSn x electrode. The carbothermal reduction method is simple, low-cost and mass-productive, which should be viable to other alloy composite materials system of rechargeable lithium ion batteries.

The Effects of the Particle Size and Active Materials on the Discharge Properties of the Li/Fe(X)S2 Electrode

Although Li/S batteries produce an efficient initial discharge capacity, they have poor cycle characteristics due to the loss of the active material that occurs in these batteries. Therefore, the material of the metal sulfide series has recently been studied as a substitute. In the present study, the possibility of fine FeS2 and Fe(x)S2 compound powders (x=Ni, Co, Mo) are examined using a mechanical alloying method, and the discharge capacity is measured. The mean particle size of the FeS2 compound powders was measured to be 600 nm at a milling time of 40 h. This data was attained through the utilization of the SEM morphologies. The initial discharge capacity of a Li/FeS2 battery was 430 mAh/g-FeS2 if into a fine powder for 20 h milled, and 890 mA/g-FeS2 if into a fine powder for 30 h milled. Moreover, it was found that if there is an addition of Ni or Co into the compound, it would increase the discharge properties. Fe(x)S2 composite powders were synthesized in order to improve the cycle life of the battery. From the charge-discharge test results, the initial discharge capacity of the Fe(Ni)S2 electrode was 845 mAh/g. The initial discharge capacity of the Fe(Co)S2 electrode was 500 mAh/g, but it showed a better cycle performance than the discharge capacity of electrodes with either additions of Ni or Mo.

Effect of additional catalytic phases imposed by sintering on the hydrogen absorption behavior of AB 2 type Zr-based alloys

The effect of microsegregated secondary phases of the Zr–Ni system on the electrochemical hydrogen absorption of a Laves phase AB 2 type alloy of composition Zr 0.9Ti 0.1(Ni 0.5Mn 0.25Cr 0.20V 0.05) 2 is studied. The activation process and discharge capacity of electrodes containing this alloy in both as-melted and annealed conditions are monitored in alkaline media along charge–discharge cycling. The as-melted material, containing microsegregated secondary phases formed during solidification, shows a higher discharge capacity and lower charging–discharging overpotentials than the annealed material. This effect is ascribed to the solubilization of the secondary catalytic phases due to the thermal treatment. To study the possibility of customizing the electrochemical properties of alloys by imposing secondary catalytic phases in a controlled way, similar tests are also carried out on a sintered composite material elaborated from powder of the annealed alloy, mixed with powder of a separately melted alloy of the Zr–Ni system, containing secondary catalytic phases, mainly Zr 7Ni 10 and Zr 9Ni 11. A sintered composite based on an alloy with low secondary catalytic phase content is also elaborated and tested for comparison. The selected base alloy is Zr(Cr 0.5Ni 0.5) 2 in annealed condition, where a major AB 2 phase with a minimum content of secondary catalytic phases is expected. The hydrogen absorption–desorption behavior for the different cases is discussed and correlated with the metallurgical characterization of the materials.

Enhanced electrochemical properties of nonstoichiometric amorphous Mg2Ni1.3 electrodes

Nonstoichiometric amorphous Mg2Ni1.3 alloys were synthesized by mechanically milling crystalline Mg2Ni alloy with Ni powders. In comparison with the stoichiometric material, the nonstoichiometric Mg2Ni1.3 phase showed a higher discharge capacity because of the amorphization of the alloy. Surface modification with graphite was also carried out for further improvement of its electrode performance. The coated powders showed a better cyclic stability because the graphite protected the Mg from oxidation. The rate capability (RC) and discharge capacity of electrodes was also markedly improved with graphite coating due to the excellent electrical conductivity and electrocatalytic activity of graphite.

Effect of the Sm content on the structure and electrochemical properties of La 1.3 − xSm xCaMg 0.7Ni 9 ( x = 0–0.3) hydrogen storage alloys

La 1.3 − x Sm x CaMg 0.7Ni 9 ( x = 0–0.3) hydrogen storage alloys were prepared by inductive melting and the effect of the Sm content on the structure and electrochemical properties was investigated in the paper. The Sm substitution for La in La 1.3 − x Sm x CaMg 0.7Ni 9 ( x = 0–0.3) alloys does not change the main phase structure (the rhombohedral PuNi 3-type structure), but leads to a shrinkage of unit cell and a decrease of hydrogen storage capacity. With the increase of the Sm content in the alloys, the maximum discharge capacity of electrode decreases from 400.2 ( x = 0) to 346.6 mAh g −1 ( x = 0.3), but the high-rate dischargeability and cycling stability is improved. After 100 cycles, the capacity retention rate increases from 75 ( x = 0) to 85% ( x = 0.3).

Structural and electrochemical properties of hydrogen storage alloys Ti 0.8Zr 0.2V 2.7Mn 0.5Cr 0.8Ni x ( x = 1.50–2.25)

In this paper, the structural and electrochemical properties of the Ti 0.8Zr 0.2V 2.7Mn 0.5Cr 0.8Ni x ( x=1.50, 1.75, 2.00, 2.25) hydrogen storage alloys have been systematically investigated. It was found by XRD and Rietveld analysis that the former two alloys were composed of a C14 Laves phase and a V-based solid solution phase, but a small amount of an impurity phase appeared in the latter two ones. The lattice parameters and cell volumes of the two main phases shrank continuously with the increasing Ni content in the alloys. Electrochemical investigations indicated that the maximum discharge capacity of the alloy electrodes decreased from 327.5 ( x=1.50) to 164.5 mAh/g ( x=2.25), while the cyclic stability improved with increasing Ni content. For the sample x=2.25, after 200 cycles the discharge capacity of the electrode still remained 96.78% of the maximum capacity. High rate dischargeability (HRD) of the alloy electrodes improved at first and then declined with increasing Ni content. Electrochemical impedance spectroscopy (EIS), linear polarization, anode polarization and potentiostatic discharge tests were employed to investigate the kinetic performance of the alloy electrodes.

Effect of electroless coating of Cu, Ni and Pd on ZrMn 0.2V 0.2Fe 0.8Ni 0.8 alloy used as anodes in Ni-MH batteries

In order to improve the electrochemical performance, the alloy represented by the composition ZrMn 0.2V 0.2Fe 0.8Ni 0.8 was microencapsulated with Cu, Ni and Pd. Microencapsulation was done prior to test electrode preparation by electroless plating method. The electrode characteristics such as electrochemical capacity and cycle life were studied for the uncoated and coated alloys. It was found that the coated alloy showed higher discharge capacity and lower activation time in comparison to the uncoated alloy. The phase composition of the alloys was characterized using X-ray diffraction (XRD) and surface morphology was studied using scanning electron microscope (SEM). It was found that the surface microencapsulation of alloy powder was effective in improving the electrode discharge capacity and in reducing the activation time.

Nanocrystalline LaNi5-type electrode materials for Ni-MHx batteries

LaNi5-based hydrogen storage alloys are a promising choice for hydrogen energy systems. In this work, nanocrystalline La(Ni,M)5 (M=Mn, Al, and Co) alloys have been synthesized by mechanical alloying (MA) followed by annealing. The discharge capacity of electrodes prepared by application of MA and annealed LaNi5 alloy powder is low. It was found that the partial substitution of Ni by Al or Mn in La(Ni,M)5 alloy leads to an increase in discharge capacity. On the other hand, cobalt substituting nickel in LaNi4−xMn0.75Al0.25Cox greatly improves the cycle life of this material. For x=0.25 the discharge capacities up to ∼260mAhg−1 were measured at current density of charging and discharging of i=40mAg−1. The studies show that electrochemical properties of Ni–MHx batteries are a function of chemical composition and microstructure of the electrode materials used. XPS studies showed that the shape of the valence band measured for the arc-melted (polycrystalline) LaNi5 is practically the same as that reported earlier for the single crystalline sample. The substitution of Ni by Al in LaNi5 leads to significant modifications of the electronic structure of the polycrystalline sample. Furthermore, the XPS valence band of the MA nanocrystalline LaNi4Al1 alloy is considerably broader compared to that measured for the polycrystalline sample. The strong modifications of the electronic structure and the significant surface segregation of lanthanum atoms in the MA nanocrystalline LaNi5-type alloys could significantly influence its hydrogenation properties.

Hydrogen absorption characteristics and electrochemical properties of Ti substituted Zr-based AB 2 alloys

The hydrogen absorption characteristics of Zr 1− x Ti x CrNi alloys, with x ranging between 0.1 and 0.4, were studied by volumetric and electrochemical techniques in order to determine their possible application as the negative electrode in nickel/metal–hydride rechargeable batteries. Electrodes of alloy powders mixed with different compacting additives were tested with respect to charge and discharge cycles in KOH solution. The effects of the electrode-compacting additive, discharge rate and temperature on the electrode discharge capacity were also investigated. The results obtained show that: (i) at 80°C the equilibrium pressures of Zr 1− x Ti x CrNi alloys with x=0.1 are 2.6 times higher than those for the unsubstituted ZrCrNi alloy, while maintaining a good hydrogen storage capacity; (ii) the Zr 0.9Ti 0.1CrNi alloy electrodes exhibit the highest discharge capacities and the best performances during fast charge–discharge cycling; (iii) the Ti substituted alloy electrodes using copper powder as compacting material show faster activation, while carbon–Teflon compacted electrodes exhibit the best cycle life behavior; (iv) for all Ti substituted alloy electrodes the discharge capacities increase with temperature.

Activation behavior of the Zr-based Laves phase alloy electrode

The poor activation of the Zr-based AB 2 Laves phase alloy hydride electrode is one of the problems retarding their commercialization. A surface treatment technique was carried out here to improve the poor activation of the alloys Zr(V 0.1 Mn 0.3Ni 0.6) 2, Zr(V 0.1Mn 0.3Ni 0.6Co 0.05) 2, ZrTi 0.1(V 0.1Mn 0.3Ni 0.6Co 0.05) 2 and ZrTi 0.1(V 0.1Mn 0.3Ni 0.6Co 0.05Cr 0.05) 2. We pre-treated the alloy powders by immersing and stirring them in solution of NH 4F/NiCl 2 to make the alloy surface clean and form a layer of nickel-rich, which has been regarded as an indispensable factor for the electrochemical activity of the alloy. It was found that the activation of the alloy electrode has been greatly improved by this method. The discharge capacity of the electrodes made from the treated alloy powder is over 345 mA h g −1 at the discharge current density of 100 mA g −1. Especially, the alloy electrode of the treated ZrTi 0.1(V 0.1Mn 0.3Ni 0.6Co 0.05Cr 0.05) 2 gives a discharge capacity of 390 mA h g −1 at the first cycle, however, the discharge capacity of the untreated alloy electrode is only 42 mA h g −1 at the first cycle. The analysis of X-ray diffraction (XRD) shows that the alloy of crystal structure is a cubic AB 2 Laves phase. The different activation property of the alloy electrode was analyzed on the basis of surface examination by scanning electron microscope (SEM), specific surface area (SSA) and X-ray photoelectron spectroscopy (XPS).

Pulverization and corrosion studies of bare and cobalt-encapsulated metal hydride electrodes

Electrochemical impedance spectroscopy was used as an in situ technique to determine the average particle size of metal hydride electrodes. Using this, the pulverization of bare and cobalt-encapsulated LaNi 4.27Sn 0.24 alloy was studied as a function of charge–discharge cycles. In the case of bare alloy, pulverization causes an exponential decay in particle size with cycling. Cobalt-encapsulated alloys do not undergo much pulverization with cycling. Bode responses obtained for bare alloy electrodes indicate the increase in particle to particle resistance with cycling. Alloy oxidation, which is responsible for the increase in particle to particle resistance is absent in the case of cobalt encapsulated alloy. Surface analysis indicates the presence of alloy segregation for bare LaNi 4.27Sn 0.24. Decrease in particle size and increase in bare alloy resistance is accompanied with severe decay in electrode discharge capacity.

Electrochemical investigations of bare and Pd-coated LaNi 4.25 Al 0.75 electrodes in alkaline solution

Electrochemical investigations were carried out on electrodes made from both bare and Pd-coated LaNi4.25Al0.75 particles. Experimental results showed that the Pd-coating significantly decreases the electrode resistance and increases the electrode discharge capacity. The electrochemical impedance spectroscopy technique was used to determine various resistive components in the electrodes and electrolyte by fitting an equivalent circuit to the experimental data. The results indicated that an electrode made from the Pd-coated alloy has much less ohmic resistance (particle-to-particle contact resistance and current collector to electrode pellet contact resistance) compared to the electrodes made from bare alloy.

Production of copper-alloy complex granules for nickel/metal hydride electrodes

We have prepared new complex granules composed of a hydrogen storage alloy and a special copper powder by use of a mechano-fusion system exerting rotation, compression and friction actions. The granules were almost spherical and porous with sizes ranging from 10 to 50 μm. The addition of a small quantity of oxidation-protective agents to the granules was effective for preventing oxidation and powder explosion. The granules were produced even under an air atmosphere. Discharge capacities of electrodes using the granules were increased by the addition of small amounts of cuprous oxide and cobalt in the preparation of the granules. The new copper-alloy complex granules showed excellent electrode performances.

The Cathodic Behavior of AgO in Alkaline Solutions

A study has been made of the discharge of to determine why only a part of the discharge capacity of is delivered at the potential of the couple and to determine the role of oxygen in this process. The difference in discharge capacity of electrodes produced by constant‐current and by constant‐potential anodizatlon also has been studied. A mechanism involving the transport of O−− ions through the electrode material and the reaction of these ions with the electrolyte is presented.